1. Technical Field
The present invention generally relates to a printing apparatus, and more particularly to a method for detecting the amount of a printing material in a printing material container that is mounted to the printing apparatus.
2. Related Art
Currently, some printing material containers which are designed to be mounted on an ink-jet-type printing apparatus are provided with sensors for detecting the amount of remaining printing material. An example of one sensor that is typically used is a piezoelectric element capable of expanding and contracting when a voltage is applied to it. After the voltage is applied, the piezoelectric element generates a residual vibration, and outputs an output signal. Thus, the printing apparatus applies a voltage to the piezoelectric element to measure the vibration frequency of the piezoelectric element contained in the output signal, and determines whether a predetermined amount of the a printing material is in the printing material container.
An example of related art is shown in Japanese Patent JP-A-2003-39707, which discloses a printing apparatus which uses a voltage applied to a piezoelectric element as a sensor. In that apparatus, the amplitude of vibration of the piezoelectric element is increased in order to give more precise measurements of the vibration frequency.
Despite these advances, however, many manufacturing errors arise during the production process of the sensors. Because of these errors, the output signal that is outputted from the sensor can vary from one sensor to another even if the same amount of a printing material remains in a printing material container. Thus, the amplitude of vibration of the piezoelectric element can be small in some cases, making it difficult to measure the vibration frequency of the piezoelectric element precisely and consistently. Consequently, it is often impossible to adequately detect the amount of the printing material contained in the printing material container.